Recent studies have shown that treatments involving nanoparticles at low concentrations have less toxic effects when used in the body and are more effective in therapies. Research shows metal and metal oxide nanoparticles have increased skin penetration by several fold, also decrease the susceptibility of infection and induce cellular proliferation in wound healing applications. Silver and zinc oxide are well known for both antimicrobial and pro-healing properties. In this study, we have tested the synergistic effect of Silver (Ag) and Zinc oxide (ZnO) nanoparticles as antimicrobial agent against bacteria and fungal organisms. Silver/Zinc oxide (Ag/ZnO) nanoparticles were synthesized using a custom built, temperature controlled microwave assisted technique. The as-synthesized nanoparticles were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques to study the crystalline structure, composition, particle size, morphology and purity. These results indicated that the as-prepared Ag nanoparticles are spherical in shape and ~20nm in sizes. The ZnO nanoparticles are typically rod shaped and the particle sizes are ~20nm in width and 100nm in length. These particles were tested for antibacterial and /or antifungal properties using standard disk diffusion and plate count assays. Results show that hybrid Ag/ZnO nanoparticles have antimicrobial activities against Escerichia coli and Candida albicans at minimum concentration of 4 mg/mL, suggesting that these nanoparticles could potentially be used to counter infections by these organisms.

Recent studies have shown that treatments involving nanoparticles at low concentrations have less toxic effects when used in the body and are more effective in therapies. Research shows metal and metal oxide nanoparticles have increased skin penetration by several fold, also decrease the susceptibility of infection and induce cellular proliferation in wound healing applications. Silver and zinc oxide are well known for both antimicrobial and pro-healing properties. In this study, we have tested the synergistic effect of Silver (Ag) and Zinc oxide (ZnO) nanoparticles as antimicrobial agent against bacteria and fungal organisms. Silver/Zinc oxide (Ag/ZnO) nanoparticles were synthesized using a custom built, temperature controlled microwave assisted technique. The as-synthesized nanoparticles were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques to study the crystalline structure, composition, particle size, morphology and purity. These results indicated that the as-prepared Ag nanoparticles are spherical in shape and ~20nm in sizes. The ZnO nanoparticles are typically rod shaped and the particle sizes are ~20nm in width and 100nm in length. These particles were tested for antibacterial and /or antifungal properties using standard disk diffusion and plate count assays. Results show that hybrid Ag/ZnO nanoparticles have antimicrobial activities against Escerichia coli and Candida albicans at minimum concentration of 4 mg/mL, suggesting that these nanoparticles could potentially be used to counter infections by these organisms.

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Judges’ Queries and Presenter’s Replies

nice work. do you have direct evidence to show the Ag/ZnO actually forms the hydrid rather than separate individuals in the product? is the antimicrobial property related to the shape of the nanostructures, e.g. spheroids vs. rods?

Thank you. Yes, High Resolution Transmission Electron Microscopy (hr-TEM)showed the Ag/ZnO NPs actually form hybrid structures. The micrographs show spherical Ag and rod like ZnO sharing the same lattice planes. X-Ray Diffraction (XRD) also showed our hybrids were composed of both nanoscale Ag and ZnO. The shape of the nanostructures does effect antimicrobial properties according to the literature. We witnessed the spherical Ag structures exhibited higher antimicrobial activity than the ZnO or hybrid Ag/ZnO NPs, however we did preform an in depth analysis on the effects of the shape of the nanostructure on the antimicrobial activities of the NPs.

I am trying to understand the data on the right hand side of the poster. If I understand it correctly, Ag>Zn0>Ag/ZnO when it comes to effect on both bacterial and fungal populations. Am I right? The concentrations at which this is effective, is that biocompatible? Is it not high enough to be toxic to living organisms (humans for example) by itself? i.e., is it therapeutically applicable? And could you explain to me how you estimate the population of bacteria (ie., what OD and plate count assays are?

A. Baskaran:
You are correct in understanding that Ag NPs have greater activity than ZnO and Ag/ZnO NPs. The target application for these materials is use in an antimicrobial cream to be applied topically. From the results the concentrations of these NPs must be adjusted to have increased biocompatibility. I do not think these materials will be toxic when used on the human skin.
Optical density is used a measurement of bacterial and fungal concentration in suspension. We measured the optical density of each microbe before and after treatment using a spectrometer and calculated the microbial concentration using simple equations. Plate count assays allow us to count colonies of the microbes. We performed a serial dilution of each microbe in a nutrient media and pipetted known volumes of the solution on to a petri dish. After incubation the colonies of microbe were quantified. We performed the plate count assays of each microbe alone, and each microbe with a treatment of our experimental materials.

We were unable to investigate the toxicity of these materials on human cells during this study. However, we have conducted a literature review and based on the knowledge gained from the literature these NPs should be safe for human use on the skin. The size and shapes of these nanoparticles are similar to those of particles used in commercially available product like sunscreen, which are not toxic to the skin. We discovered simple mixture of silver and ZnO does not behave the same way as the hyrids produced using microwave synthesis.

The microwave synthesis technique involves irradiating pre-cursor materials to produce Ag, ZnO and hybrid Ag/ZnO NPs. Pre-cursors were made into a solution, irradiated for 10 minutes at 300W power under temperature control. The resulting solution was then washed, the particles collected and then dried. The final product was a fine powder. One of the goals of this research was to fabricate nanomaterials using a technique that was both easy and rapid. This goal was achieved using the microwave synthesis technique.

We hypothesized that properties of Ag/ZnO hybrids would work synergistically to function as an antimicrobial agent effective against both bacteria and fungi. Results from the experimentation with a mixture of Ag and ZnO showed insignificant antimicrobial activity.

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Presentation Discussion

Joseph III

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May 21, 2013 | 09:18 a.m.

Great initiative in using nanoparticles as antimicrobial agents; particularly important for development of anti-yeast drugs as those microorganisms are not responsive to anti-bacterial antibiotics.